linux-kernel - Re: [PATCHv4 1/2] ARM: imx53: add secure-reg-access support for PMU

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Message-ID: <20180528022652.GA3143@dragon>
Date:   Mon, 28 May 2018 10:26:54 +0800
From:   Shawn Guo <shawnguo@...nel.org>
To:     Sebastian Reichel <sebastian.reichel@...labora.co.uk>
Cc:     Sascha Hauer <kernel@...gutronix.de>,
        Fabio Estevam <fabio.estevam@....com>,
        Will Deacon <will.deacon@....com>,
        Mark Rutland <mark.rutland@....com>,
        Russell King <linux@...linux.org.uk>, Ian Ray <ian.ray@...com>,
        Nandor Han <nandor.han@...com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        kernel@...labora.com
Subject: Re: [PATCHv4 1/2] ARM: imx53: add secure-reg-access support for PMU

On Tue, Feb 27, 2018 at 11:17:12AM +0100, Sebastian Reichel wrote:
> Hi,
> 
> On Tue, Feb 27, 2018 at 09:10:34AM +0800, Shawn Guo wrote:
> > On Mon, Feb 26, 2018 at 02:47:41PM +0100, Sebastian Reichel wrote:
> > > On Sat, Feb 24, 2018 at 03:45:44PM +0800, Shawn Guo wrote:
> > > > On Mon, Feb 12, 2018 at 01:39:44PM +0100, Sebastian Reichel wrote:
> > > > > On i.MX53 it is necessary to set the DBG_EN bit in the
> > > > > platform GPC register to enable access to PMU counters
> > > > > other than the cycle counter.
> > > > > 
> > > > > Signed-off-by: Sebastian Reichel <sebastian.reichel@...labora.co.uk>
> > > > > ---
> > > > >  arch/arm/mach-imx/mach-imx53.c | 39 ++++++++++++++++++++++++++++++++++++++-
> > > > >  1 file changed, 38 insertions(+), 1 deletion(-)
> > > > > 
> > > > > diff --git a/arch/arm/mach-imx/mach-imx53.c b/arch/arm/mach-imx/mach-imx53.c
> > > > > index 07c2e8dca494..658e28604dca 100644
> > > > > --- a/arch/arm/mach-imx/mach-imx53.c
> > > > > +++ b/arch/arm/mach-imx/mach-imx53.c
> > > > > @@ -28,10 +28,47 @@ static void __init imx53_init_early(void)
> > > > >  	mxc_set_cpu_type(MXC_CPU_MX53);
> > > > >  }
> > > > >  
> > > > > +#define MXC_CORTEXA8_PLAT_GPC 0x63fa0004
> > > > 
> > > > The base address should be retrieved from device tree.
> > > 
> > > DT has no entry for 0x63fa0000-0x63fa3fff. iMX53 TRM lists it as "ARM Platform"
> > > with 8 platform specific 32 bit registers. Do you think it's worth the trouble
> > > adding a new binding? Do you have a suggestion for a compatible value?
> > 
> > Looking at it more closely, I feel that patching every single platform
> > which needs to set up additional register for secure-reg-access support
> > doesn't really scale.  Can we have pmu driver do it with a phandle in
> > DT pointing to the register and bit that need to be configured?
> 
> The PMU driver used to have a feature for initialising platform
> specific bits, but it is currently being removed to make the PMU
> code more maintainable. My understanding is, that it's very uncommon
> to require platform specific setup to get secure-reg-access working.
> I.e. it is not needed for newer iMX platforms.

Are you saying this is a very specific setup required by i.MX53 only?
In that case, I can live with it.

Shawn